Head pressure biased control valve

ABSTRACT

An automatic control for preventing freezing of the evaporator of an air conditioner including a piston type main valve within the compressor inlet. One side of the main valve is exposed to a control pressure in a space connected by a port to compressor inlet. A control valve in this port is operated by an expandable, evacuated bellows which opens and closes the valve to maintain a substantially constant pressure in the space. A plunger of small cross section is aligned with the control valve and is exposed to the high pressure discharge of the compressor to tend to open the control valve in response to increased discharge pressure. This lowers the control pressure and allows the main valve to open earlier than during lower discharge pressure operation.

United States Patent i191 Heidorn HEAD PRESSURE BIASED CONTROL VALVE Jan. 8, 1974 [57] ABSTRACT An automatic control for preventing freezing of the evaporator of an air conditioner including a piston type main valve within the compressor inlet. One side of the main valve is exposed to a control pressure in a space connected by a port to compressor inlet. A control valve in this port is operated by an expandable, evacuated bellows which opens and closes the valve to maintain a substantially constant pressure in the space. A plunger of small cross section is aligned with the control valve and is exposed to the high pressure discharge of the compressor to tend to open the con trol valve in response to increased discharge pressure. This lowers the control pressure and allows the main valve to open earlier than during lower discharge pressure operation.

4 Claims, 4 Drawing Figures PA IEMED M E I Y 3,783,634"

U) a I g EVAPORATOR r om FREEZE LINE D-U') LL! g 4 LJJCL I AMBIENT DISCHARGE TEMPERATURE PRESSURE HEAD PRESSURE BIASED CONTROL VALVE This invention relates to automatic temperature controls for air conditioning evaporators.

When refrigerant compressors are driven by a variable speed internal combustion engine that is commonly used with auto air conditioning systems, there is tendency for frost to accumulate on the evaporator during relatively low ambient temperature operation. This is because under conditions of high compressor speed and relatively small heat loads on the evaporator, the refrigerant pressure in the evaporator drops considerably. This is because of decreased boiling of refrigerant and increased evacuation by the compressor. Freezing temperatures of the evaporator which allow frost to form correspond to low refrigerant pressure.

More particularly, under some operating conditions of the air conditioning system, the refrigerant expansion means which may be a small diameter restrictor cannot supply sufficient liquid refrigerant to the evaporator to maintain the evaporators pressure above the freezing level. These conditions correspond to many low ambient temperature conditions. When the expansion valve cannot supply enough refrigerant, frost may accumulate on the evaporator. The frost may eventually block the air flow through the evaporator which will only compound the problem and seriously reduce the heat exchange from the air to the evaporator.

The subject air conditioning system includes an automatic throttling valve in the compressor inlet with a valve member reciprocal within a bore formed in the compressor end housing. The throttling valve opens and closes to maintain pressure and therefore sufficient temperature in the evaporator to prevent frost accumulation thereon. Closing the throttling valve reduces the refrigerant flow into the compressor and from the evaporator to maintain the pressure.

For more efficient operation of a throttled air conditioning system, the refrigerant pressure in the evaporator may be decreased below the freeze value as the heat load on the evaporator increases. This is because the increased heat transfer between the air flowing through the evaporator and the evaporator refrigerant produces a temperature gradient between the evaporator fins and the fluid carrying tubes of the evaporator. Because frost formation on the fins rather than the tubes is critical, the refrigerant temperature in the evaporator may drop below freezing while the tin temperature remains above freezing under higher ambient temperature operation.

It has been observed that the discharge pressure at the compressor outlet increases somewhat proportionally with increases in ambient temperature. Thus, as the ambient temperature which flows through the evaporator increases, the compressor .discharge pressure also increases. The present invention utilizes a discharge pressure actuated override control on the throttling valve to permit refrigerant temperature in the evaporator to drop below the normal freeze level as discharge pressure increases. This decreasing refrigerant pressure in the evaporator as the discharge pressure in the increases closely follows the freeze characteristics of the evaporator and permits more efficient use of low evaporator pressures as the ambient temperature and the heat load increase.

Therefore, it is an object of the present invention to provide an automatic control for refrigerating apparatus including a throttling valve within a bore in the compressor housing which connects the evaporator outlet and the compressor inlet and a discharge pressure responsive override tending to openthe throttling valve in response to increased discharge pressure.

It is a further object of the invention to provide an automatic control for the evaporator of an air conditioning system including a reciprocal throttling valve within the compressor housing located between the evaporator outlet and the compressor inlet and actuated by a pressure differential produced by operation of a bleed valve in a port between the compressor inlet and a space adjacent one side of the reciprocal valve and further including a discharge pressure actuated override which tends toopen the port with increases in the discharge pressure and to evacuate the space adjacent the throttling valve andrcause the throttling valve to open at decreasing evaporator pressures. i

It is a still further object of the-present invention to provide an integral pressure responsive throttling valve and compressor housing for an automotive air conditioning system including a, discharge pressure actuated override which tends to open the throttling valve under decreasing evaporator pressures with increases in discharge pressure.

Further objects and advantages of the present invention will be apparent from the following detailed description, reference being had to the accompanying drawings in which a preferred embodiment of the invention is clearly shown.

IN THE DRAWINGS FIG. 1 is a diagrammatic view of an automobile air conditioning system showing the integral compressor and throttling valve assembly in end view;

FlG. 2 is an enlarged and fragmentary view of the compressor head which encloses the throttling valve;

FIG. 3 is a sectional view taken along section line 3-3 in FIG. 2 and looking in the direction of the arrows; and i FIG. 4 is a plot of control pressure in the throttling valve vs. ambient temperature and discharge pressure.

Referring to FIG. 1, there is illustrated an end view of an automotive refrigerant compressor 10. The compressor 10 is of the type shown in US. Pat. No. 3,057,545 issued on Oct. 9, 1962 to Ransom et al and assigned to General Motors Corporation. It includes a cylindrical housing l2 with an end cover 14. Refrigerant is compressed by reciprocally moved pistons within the compressor 10 and is discharged through an outlet 16. It then passes through a conduit 18 to a condenser 20. From the condenser 20 the refrigerant flows to an expansion means 22 which may be a small diameter, short length passage 24 'as illustrated. Refrigerant flows from the expansion means 22 to an evaporator 26 where it absorbs heat from air flowing into the automobile passenger compartment. It then flows from evaporator 26 through a conduit 28 and into an accumulator 30. The accumulator 30' collects liquid refrigerant which happens to pass through the evaporator 26. An upwardly extending outlet 32 within the accumulator 30 picks up refrigerant vapor which flows through the suction conduit 34 to an inlet 36.

' Refrigerant enters the compressor 10 through inlet 36 as best shown in enlarged FIG. 2. Inlet 36 houses piston type throttling valve 38 which is reciprocal within bore 40. In the illustrated closed position, valve 38 is moved to the right where it is restrained by a spring retainer 42. The spring retainer 42 has an offset central portion 44 which supports one end of coil spring 46 which bears against a first side 48 of the valve 38. When the valve 38 is moved to the left from its closed position, refrigerant flows from inlet 36 around the valve and into an annular channel 50 which conveys it to the sump portion of the compressor prior to compression. The passage 50 is further illustrated in FIG. 3.

The valve 38 is normally held against the spring retainer 42 into a closed position by a coil spring 52 located within a space 54 on the second side 56 of the piston valve 38. The space 54 is fluidly communicated with the inlet 36 by a small diameter bleed ,port 58 through piston 38. Strainer or filter 60 prevents foreign matter from clogging port 58.

The space 54 is evacuated through a control port 62 connected by a passage 64 to the sump portion of the compressor from which the refrigerant is picked up by the compressor for pressurization. Control port 62 and passage 64 are formed in an end plug 66 which is threaded at 68 into housing 14. An O-ring 70 in a groove 72 in the plug 66 prevents fluid leakage between space 54 and passage 64.

The port 62 is normally closed by a control valve 74 having a tapered end portion 76 which extends into the port. The midportion of the control valve 74 is fastened to one end 78 of a sealed and expandable bellows 80. The other end 82 of the bellows 80 is fastened to a retainer 84 whose outer edge 86 engages the wall of bore 40 to support the bellows 80. End 88 of spring 52 seats against the retainer 84. The interior of bellows 80 is evacuated and contains a spring 90 which extends between the ends of the bellows. A conbination guide and stop member 94 at one end of bellows 80 receives a reduced diameter portion 96 of piston 74. The stop 94 prevents the control valve 74 from being moved more than a desired distance from port 62 when pressure within chamber'54 increases.

. During operation of the air conditioning system under relatively moderate ambient temperatures, such as between 65 to 75 F., the expansion means 22 delivers sufficient liquid refrigerant to the evaporator 26 to be boiled or vaporized and returned to the compressor through the conduit 28, accumulator 30 and conduit 34. Throttling valve 38 is moved to the left in FIG. 2 by the pressure differential between inlet 36 and space 54 to permit refrigerant to flow to the compressor sump. The refrigerant pressure within the control space 54 is maintained at a substantially constant value by leakage through bleed port 58 and the opening and closing of control valve 74 which regulates the evacuation of space 54 in conjunction with fluid passage means either in end cover 14 or retainer 84 which extends through space 54. When the control pressure in space 54 tends to become greater than desired, the bellows contracts and opens the control port 62 to discharge some of the refrigerant. When the control pressure tends to be less than desired, the bellows expands to block port 62 and permits refrigerant to flow through the filter 60 and bleed port 58 into the space 54. Consequently, the pressure acting against the first face 48 of valve 38, the control pressure in space 54 acting against face 56 and the action of springs 46 and 52 governs the position of the valve 38. As the pressure in the inlet 36 which closely corresponds to the evaporator pressure tends to drop below a freezing pressure (about 28 psig when Freon 12 refrigerant is used) the pressure differential between the space 54 and inlet 36 acts on the valve 38 to close off the communication between inlet 36 and passage 50. Resultantly, the pressure within the evaporator is increased to prevent frost form accumulating on the tinned surfaces.

As previously stated, the action of bellows and valve 74 controls the throttling valve to normally maintain the refrigerant pressure in the evaporator at about 28 psig to prevent frost accumulation on the evapora' tors fin surfaces. As ambient temperature increases to a relatively high value, say in a range of 80 to F., it has been observed that evaporator pressures lower thanggpsjg can be tolerated without any frost forming on the finned surfaces. This is because the increased rate of heat input to the evaporator from the relatively hot air produces a significant temperature difference between the finned surfaces and the refrigerant carrying tube surfaces. FIG. 4 illustrates this observation by plotting the pressure in the evaporator against the ambient temperature for a given evaporator and refrigerant system. The broken line represents the evaporator freeze line. Below this line frost may accumulate on the evaporator at corresponding pressures and ambient temperatures. The solid line indicates a desired operation of the throttling valve to maintain a pressure. in the evaporator slightly above the evaporator freezeline. This prevents frost accumulation on the fin surfaces of the evaporator.

It is known that the refrigerant discharge pressure increases with increases in ambient temperature for a given air conditioning system, compressor speed and refrigerant. This explains the dual labelling of the horizontal axis with both ambient temperature and discharge pressure shown in FIG. 3.

The subject throttling valve utilizes the relation between ambient temperature and compressor discharge pressure to decrease the evaporator pressure and temperature as the ambient temperature increases. Specifically, a passage 98 in plug 66 is communicated-by groove 100 and another passage (not visible) with the high pressure discharge of the compressor. Passage 98- intersects a bore 102 which is aligned with the control valve 74. An override plunger 104 is reciprocally mounted within the bore 102. One end 106 of plunger 104 fluidly communicates with passage 98 and is exposed to the high pressure refrigerant. The other end of the plunger 104 is aligned adjacent end 76 of bleed valve 74. As the discharge pressure of the compressor increases corresponding to increased ambient temperatures, the plunger 104 is moved to the right in FIG. 2 against control valve 74 to cause evacuation of space 54 through the port 62 and passage 64. This lowers the control pressure within the space or control chamber 54 and causes the valve 38 to move easily to the left toward an open position. When the valve 38 moves to the left, refrigerant is evacuated from the evaporator and the pressure decreases. This decrease in evaporator pressure lowers the temperature of the refrigerant in the evaporator tubes. However, the finned sufaces of the evaporator do not drop below 32 F. due to the increased heat transfer under high ambient temperature operating conditions. The O-rings 108 and 110 in grooves 112 and 114 prevent refrigerant leakage between the passages 64 and 98 and atmosphere.

While the embodiment of the invention as described above and illustrated in the drawings constitutes a preferred form, other forms may be adapted.

What is claimed is as follows:

1. An automotive air conditioning system having an improved evaporator control comprising: a refrigerant compressor connected in series fluid flow relation with a condenser, an expansion means, and an evaporator; said compressor having a housing portion with an inlet for receiving refrigerant from said evaporator; flow control means between said inlet and including a main valve member for restricting the flow of refrigerant from said evaporator to the interior of said compressor, one side of said main valve member exposed to refrigerant from said evaporator, the second side partially defining an adjacent control space; a bleed port in in said main valve connecting said space to said inlet; a control port and a control valve therein regulating refrigerant flow between the space and the interior of said compressor; pressure responsive means in said control space operably connected to said control valve for maintaining a substantially constant pressure in said space whereby said main valve is operated to control the refrigerant pressure in said evaporator to prevent frost formation thereon; a high pressure port in said housing portion connected to the compressor outlet; fluid pressure actuated means exposed to high pressure fluid in said port and operably connected to-said control valve for causing said control valve to be opened in response to increases in the outlet pressure whereby said control port and said control space are communicated to evacuate refrigerant therefrom and reduce pressure in said control space thereby permitting said main valve to open at increasingly lower evaporator pressures and temperatures in proportion to increasing outlet pressures.

2. An automotive air conditioning system having an improved evaporator control comprising: a refrigerant compressor connected in series fluid flow relation with a condenser, an expansion means, and an evaporator; said compressor having a housing portion with an inlet for receiving refrigerant from said evaporator; flow control means between" said inlet and including a main valve member for restricting the flow of refrigerant from said evaporator to the interior of said compressor, one side of said main valve member exposed to refrigerant from said evaporator, the second side partially defining an adjacent control space; a bleed port in said main valve connecting said space to said inlet; a control port and a control valve therein regulating refrigerant flow between the space and the interior of said compressor; pressure responsive means in said control space operably connected to said control valve for maintaining a substantially constant pressure in said space whereby said main valve is operated to control the refrigerant pressure in said evaporator to prevent frost formation thereon; a high pressure port in said housing portion extending between the compressor outlet and one end of a reciprocal plunger which is mounted in a bore in said housing portion; the other end of said plunger being in operative alignment with said control valve to open said valve in response to increases in the compressor outlet pressure whereby said control port and said control space are fluidly communicated to evacuate refrigerant therefrom and reduce pressure in said control space thereby permitting said main valve to open at an increasingly lower evaporator pressures and temperatures in proportion to increasing outlet pressures.

3. An automotive air conditioning system having an improved evaporator control comprising: a refrigerant compressor connected in series fluid flow relation with a condenser, an expansion means, and an evaporator; said compressor having a housing portion with an inlet for receiving refrigerant from said evaporator; flow control means between said inlet and including a main valve member for restricting the flow of refrigerant from said evaporator to the interior of said compressor, one side of said main valve member exposed to refrigerant from said evaporator, the second side partially defining an adjacent control space; a bleed port in said main valve connecting said space to said inlet; a control port and a control valve therein regulating refrigerant flow between said space and the interior of said compressor; a sealed bellows supported in said space operably connected to said control valve for maintaining a substantially constant pressure in said space by expan sion and contraction in response to pressure in said control space whereby said main valve is operated to control the refrigerant pressure in said evaporator to prevent frost formation thereon; a high pressure port in said housing portion extending between the compressor outlet and one end of a reciprocal plunger which is mounted in a bore in said housing portion; the other end of said plunger being in operative alignment with said control valve to open said valve in response to increases in the compressor outlet pressure whereby said control port and said control space are communicated to evacuate refrigerant therefrom and reduce pressure in said control space thereby permitting said main valve to open at increasingly lower evaporator pressures and temperatures in proportion to increasing outlet pressures. i

4. An automotive air conditioning system having an improved evaporator control comprising: a refrigerant compressor connected in series fluid flow relation with a condenser, an expansion means, and an evaporator; said compressor having a housing portion with an inlet for receiving refrigerant from said evaporator; flow control means between said inlet and including a main valve member for restricting the flow of refrigerant from said evaporator to the interior of said compressor,

one side of said main valve member exposed to refrigerant from said evaporator, the second side partially defining an adjacent control space; a bleed port in said main valve connecting said control space and said inlet; a control port and a control valve therein regulating refrigerant flow between said space and the interior of said compressor; a sealed and expandable bellows supported in said space operably connected to said control valve for maintaining a substantially constant pressure in said space by expansion and contraction in response to pressure in sais control space whereby said main valve is operated to control the refrigerant pressure in said evaporator to prevent frost formation thereon; a high pressure port in said'housing portion extending between the compressor outlet and one end of a reciprocal plunger which is mounted in a bore in said housing portion; the other end of said plunger being in operative alignment with said control valve to open said valve in response to increases in the outlet pressure whereby said control port and said control space are communicated to evacuate refrigerant therefrom and reduce pressure in said control space thereby permitting said main valve to open at increasingly lower evap orator pressures and temperatures in proportion to increasing outlet pressures; stop means in said sealed bellows for operably engaging said control valve to prevent'said pressure actuated plunger from contracting said bellows beyond a predetermined amount. 

1. An automotive air conditioning system having an improved evaporator control comprising: a refrigerant compressor connected in series fluid flow relation with a condenser, an expansion means, and an evaporator; said compressor having a housing portion with an inlet for receiving refrigerant from said evaporator; flow control means between said inlet and including a main valve member for restricting the flow of refrigerant from said evaporator to the interior of said compressor, one side of said main valve member exposed to refrigerant from said evaporator, the second side partially defining an adjacent control space; a bleed port in in said main valve connecting said space to said inlet; a control port and a control valve therein regulating refrigerant flow between the space and the interior of said compressor; pressure responsive means in said control space operably connected to said control valve for maintaining a substantially constant pressure in said space whereby said main valve is operated to control the refrigerant pressure in said evaporator to prevent frost formation thereon; a high pressure port in said housing portion connected to the compressor outlet; fluid pressure actuated means exposed to high pressure fluid in said port and operably connected to said control valve for causing said control valve to be opened in response to increases in the outlet pressure whereby said control port and said control space are communicated to evacuate refrigerant therefrom and reduce pressure in said control space thereby permitting said main valve to open at increasingly lower evaporator pressures and temperatures in proportion to increasing outlet pressures.
 2. An automotive air conditioning system having an improved evaporator control comprising: a refrigerant compressor connected in series fluid flow relation with a condenser, an expansion means, and an evaporator; said compressor having a housing portion with an inlet for receiving refrigerant from said evaporator; flow control means between said inlet and including a main valve member for restricting the flow of refrigerant from said evaporator to the interior of said compressor, one side of said main valve member exposed to refrigerant from said evaporator, the second side partially defining an adjacent control space; a bleed port in said main valve connecting said space to said inlet; a control port and a control valve therein regulating refrigerant flow between the space and the interior of said compressor; pressure responsive means in said control space operably connected to said control valve for maintaining a substantially constant pressure in said space whereby said main valve is operated to control the refrigerant pressure in said evaporator to prevent frost formation thereon; a high pressure port in said housing portion extending between the compressor outlet and one end of a reciprocal plunger which is mounted in a bore in said housing portion; the other end of said plunger being in operative alignment with said control valve to open said valve in response to increases in the compressor outlet pressure whereby said control port and said control space are fluidly communicated to evacuate refrigerant therefrom and reduce pressure in said control space thereby permitting said main valve to open at an increasingly lower evaporator pressures and temperatures in proportion to increasing outlet pressures.
 3. An automotive air conditioning system having an improved evaporator control comprising: a refrigerant compressor connected in series fluid flow relation with a condenser, an expansion means, and an evaporator; said compressor having a housing portion with an inlet for receiving refrigerant from said evaporator; flow control means between said inlet and including a main valve member for restricting the flow of refrigerant from said evaporator to the interior of said compressor, one side of said main valve member exposed to refrigerant from said evaporator, the second side partially defining an adjacent control space; a bleed port in said main valve connecting said space to said inlet; a control port and a control valve therein regulating refrigerant flow between said space and the interior of said compressor; a sealed bellows supported in said space operably connected to said control valve for maintaining a substantially constant pressure in said space by expansion and contraction in response to pressure in said control space whereby said main valve is operated to control the refrigerant pressure in said evaporator to prevent frost formation thereon; a high pressure port in said housing portion extending between the compressor outlet and one end of a reciprocal plunger which is mounted in a bore in said housing portion; the other end of said plunger being in operative alignment with said control valve to open said valve in response to increases in the compressor outlet pressure whereby said control port and said control space are communicated to evacuate refrigerant therefrom and reduce pressure in said control space thereby permitting said main valve to open at increasingly lower evaporator pressures and temperatures in proportion to increasing outlet pressures.
 4. An automotive air conditioning system having an improved evaporator control comprising: a refrigerant compressor connected in series fluid flow relation with a condenser, an expansion means, and an evaporator; said compressor having a housing portion with an inlet for receiving refrigerant from said evaporator; flow control means between said inlet and including a main valve member for restricting the flow of refrigerant from said evaporator to the interior of said compressor, one side of said main valve member exposed to refrigerant from said evaporator, the second side partially defining an adjacent control space; a bleed port in said main valve connecting said control space and said inlet; a control port and a control valve therein regulating refrigerant flow between said space and the interior of said compressor; a sealed and expandable bellows supported in said space operably connected to said control valve for maintaining a substantially constant pressure in said space by expansion and contraction in response to pressure in sais control space whereby said main valve is operated to control the refrigerant pressure in said evaporator to prevent frost formation thereon; a high pressure port in said housing portion extending between the compressor outlet and one end of a reciprocal plunger which is mounted in a bore in said housing portion; the other end of said plunger being in operative alignment with said control valve to open said valve in response to increases in the outlet pressure whereby said control port and said control space are communicated to evacuate refrigerant therefrom and reduce pressure in said control space thereby permitting said main valve to open at increasingly lower evaporator pressures and temperatures in proportion to increasing outlet pressures; stop means in said sealed bellows for operably engaging said control valve to prevent said pressure actuated plunger from contracting said bellows beyond a predetermined amount. 